Jazz

I would choose Dave Brubeck - Take Five

I think Take Five encapsulates a lot. The history of Jazz. The sound of Jazz. And the influence of Jazz. Jazz is the genre that provides for basically 90% of every sample ever covered in any other genre. I don't think you can actually count how many times Take Five was covered or Dave Brubeck songs in general. Same goes for songs like Cantaloupe Island.

The problem with Jazz is that it's meant to not encapsulate anything but... everything, so we will need to try more.

Afterwards the person needs to listen to Dave Brubeck - Bluette

Then Miles Davis - So What?*

Then The Seatbelts - Tank!

If the person still doesn't like Jazz, I will make him listen to Dizzie Gillespie and if that doesn't work I will kill him.

Edit: After the overwhelming amount of suggestions for this list, I decided to switch John Coltrane's Giant Steps with Miles Davis' So What*. 3 people actually love Miles Davis so much that they sent me personal messages asking me to include him in this post, 2 of them actually even specifically asking for the same song, finding it unfair that I included John Coltrane instead! (And they are not alone, considering that other people asked for this in the comments, too!) I want to mention, that I would find My favourite Things a better choice, though. ;)